In this paper we will describe some problems related to the defini-tion of a set of data categories as well as to the import and merging of data from various resources. First, we illustrate how organizing a taxonomy of data cate-gories is facilitated by using the principles for creating a terminological ontolo-gy (or concept system). Next, we discuss how multiple terminological entries referring to the same concept can be identified with the purpose of merging them.